You can do this with Sticky Posts feature in WordPress.
When you make a post sticky, it shows up above your new posts. As name suggests, that particular post will stick at top, first in the row for as long as you want.
Sticky Posts is a feature introduced with Version 2.7. A check box is
included on the Administration > Posts > Add New Screen (In the
Publish panel under Visibility. Click edit to see the checkbox). If
checked, the post will be placed at the top of the front page of
posts, keeping it there until new posts are published. Please notice
that this feature is only available for the built-in post type post
and not for custom post types.